drop uuid and use modified nanoid

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

util/id/id.go

@@ -0,0 +1,108 @@
+package id
+
+import (
+	"crypto/rand"
+	"errors"
+	"math"
+)
+
+// DefaultAlphabet is the alphabet used for ID characters by default
+var DefaultAlphabet = []rune("6789BCDFGHJKLMNPQRTWbcdfghjkmnpqrtwz")
+
+// DefaultSize is the size used for ID by default
+var DefaultSize = 16
+
+// getMask generates bit mask used to obtain bits from the random bytes that are used to get index of random character
+// from the alphabet. Example: if the alphabet has 6 = (110)_2 characters it is sufficient to use mask 7 = (111)_2
+func getMask(alphabetSize int) int {
+	for i := 1; i <= 8; i++ {
+		mask := (2 << uint(i)) - 1
+		if mask >= alphabetSize-1 {
+			return mask
+		}
+	}
+	return 0
+}
+
+// New returns new id or error
+func New(opts ...Option) (string, error) {
+	options := NewOptions(opts...)
+
+	if len(options.Alphabet) == 0 || len(options.Alphabet) > 255 {
+		return "", errors.New("alphabet must not be empty and contain no more than 255 chars")
+	}
+	if options.Size <= 0 {
+		return "", errors.New("size must be positive integer")
+	}
+
+	chars := options.Alphabet
+
+	mask := getMask(len(chars))
+	// estimate how many random bytes we will need for the ID, we might actually need more but this is tradeoff
+	// between average case and worst case
+	ceilArg := 1.6 * float64(mask*options.Size) / float64(len(options.Alphabet))
+	step := int(math.Ceil(ceilArg))
+
+	id := make([]rune, options.Size)
+	bytes := make([]byte, step)
+	for j := 0; ; {
+		_, err := rand.Read(bytes)
+		if err != nil {
+			return "", err
+		}
+		for i := 0; i < step; i++ {
+			currByte := bytes[i] & byte(mask)
+			if currByte < byte(len(chars)) {
+				id[j] = chars[currByte]
+				j++
+				if j == options.Size {
+					return string(id[:options.Size]), nil
+				}
+			}
+		}
+	}
+}
+
+// Must is the same as New but panics on error
+func Must(opts ...Option) string {
+	id, err := New(opts...)
+	if err != nil {
+		panic(err)
+	}
+	return id
+}
+
+// Options contains id deneration options
+type Options struct {
+	Alphabet []rune
+	Size     int
+}
+
+// Option func signature
+type Option func(*Options)
+
+// Alphabet specifies alphabet to use
+func Alphabet(alphabet string) Option {
+	return func(o *Options) {
+		o.Alphabet = []rune(alphabet)
+	}
+}
+
+// Size specifies id size
+func Size(size int) Option {
+	return func(o *Options) {
+		o.Size = size
+	}
+}
+
+// NewOptions returns new Options struct filled by opts
+func NewOptions(opts ...Option) Options {
+	options := Options{
+		Alphabet: DefaultAlphabet,
+		Size:     DefaultSize,
+	}
+	for _, o := range opts {
+		o(&options)
+	}
+	return options
+}